Aqueous emulsion polymers, also called latexes or polymer dispersions, are known and used in both clear and pigmented coatings. For example, aqueous emulsion polymers are used in interior and exterior architectural coating compositions, general metal coating compositions, and even adhesive compositions, among others. Aqueous emulsion polymers can be formed by aqueous emulsion polymerization of ethylenically unsaturated monomers such as styrene and its derivatives; acrylic and methacrylic acids; alkyl acrylates, methacrylates, and hydroxyl-substituted derivatives; vinyl esters including vinyl acetate, vinyl isopropyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl neo-nonanoate, 2-ethyl hexanoate, vinyl neo-decanoate, vinyl neoendecanoate, vinyl neo-dodecanoate and mixtures thereof; acrylonitrile; glycidyl acrylates and methacrylates, among others.
There are a large number of independent variables that can be manipulated in designing aqueous emulsion polymers. This renders the preparation of improved aqueous emulsion polymers technically challenging. The aqueous emulsion polymers used in aqueous coating compositions must be hard enough to resist physical and chemical forces, but at the same time, soft enough to form a continuous film. Film durability, water resistance, and chemical resistance are provided by hard polymers with glass transition temperatures (Tg) above ambient temperature. However, to be film-forming, these aqueous emulsion polymers must have a minimum filming temperature (MFT) at or below ambient temperature, to allow for fusion of the polymer particles into a continuous film.
While a variety of aqueous emulsion polymers have been described in the art, there is a continuing need for polymer dispersions containing emulsion polymers which provide a coating or film having excellent performance properties such as good scrub resistance, good wet adhesion, blocking resistance at elevated temperature, high gloss, water and chemical resistance, and excellent low temperature film formation, all with minimal volatile organic compound (VOC) levels.